The Internet has become a pervasive medium that allows worldwide access to multi-media content including audio, video, graphics and text, that typically requires a large bandwidth for downloading and viewing. Most Internet Service Providers (“ISPs”) allow customers to connect to the Internet via a serial telephone line from a Public Switched Telephone Network (“PSTN”). Conventional PSTN connections typically provide data rates ranging from 14,400 bps to 56,000 bps. These data rates are typically much slower than the data rates available on a coaxial cable or HFC cable system in a cable television network.
A Cable Television Network, also known as a Community Access Television (CATV) network, typically consists of a traditional coaxial cable tree and branch or HFC network. A headend controller manages downstream and upstream bandwidth resources that have been assigned to a cable modem service. The headend controller may simultaneously provide service to and control over one or more downstream channels and one or more upstream channels. A cable modem is typically located at the home of a CATV network subscriber. Cable modems receive information and instructions via signals received on the downstream channel by the headend controller. A cable modem transmits information and replies via signals on an upstream channel to the headend controller.
Communication between the headend and customer premise equipment (CPE) such as a cable modem, may be accomplished via RF modulation of data in the forward path (headend to CPE) that all CPE may demodulate and process. The headend may also communicate control messages and timing references to the CPE to enable the CPEs to transmit bursts of data in the return path (CPE to headend). The bursts are synchronized so that the headend may demodulate and properly process the received data.
Advantageously, transmission of signals by coaxial cable introduces little distortion at high data transmission rates. However, the coaxial cable may significantly attenuate the transmitted signal. Conventionally, amplifiers are spaced along the coaxial cable throughout a HFC network to provide necessary signal enhancement. Other active devices such as for example fiber nodes may also be present in an HFC network. Failure of the primary power source in such a system removes power from these active devices, effectively shutting down the HFC network. Such a network failure may be unacceptable for voice over cable applications that require strict system availability. In addition, the government also requires system availability in certain locations even if there is a loss of the primary commercial power source.
Therefore, standby power system are typically utilized to provide auxiliary power to active network components as well as to certain customer premise equipment in the event of failure of the primary source of power. Standby systems typically include a storage battery, that is maintained at full charge by current drawn from the coaxial cable. Following failure of the primary source, the standby system delivers power immediately to avoid disruption of service over the CATV network.
However, standby power systems are extremely expensive. Each standby power unit typically includes a rectifier, battery, regulator, inverter and, in many cases, the logic circuitry for turning the standby unit on and off. Secondly, because of the circuit complexity, maintenance and replacement costs are high. Thirdly, also because of the circuit complexity, reliability is not high. Therefore, to reduce the cost of maintaining a standby power system, service providers attempt to minimize the overall power load of equipment coupled to a HFC network.
The RF circuitry and digital logic required to support and maintain bi-directional communication between customer premise equipment and the cable headend over a HFC network consumes significant amounts of power. However, the DOCSIS specification does not provide the ability to interface with equipment having power management systems. In fact, DOCSIS prohibits device disconnection, specifically requiring DOCSIS network equipment be available at all times to respond to maintenance requests. However, in lifeline powering situations, equipment that must remain available during a power outage strain the ability of the HFC plant to supply power to all network components. Therefore, it would be advantageous to reduce the power of DOCSIS compatible customer premise equipment to ensure efficient operation of the HFC plant during lifeline or power out situations.
Conventional power management techniques typically realize power savings by disabling the tuning and demodulation circuits. When returning to the full power active state, the equipment whose demodulation circuits have been disabled must re-synchronize to the CMTS to resume accurate bi-directional communications over the HFC network. Therefore, applications that have strict latency requirements may not be supported by such conventional systems. An example of an application that is adversely affected by this power management technique is voice telephony. In addition, DOCSIS specifically prohibits the incorporation of network equipment that is not available at all times to respond to maintenance requests. Therefore, it would be advantageous to provide a power management system that reduces the power of bi-directional communications equipment without introducing significant latency.